.content_ul{
    width: 100%;
    margin-bottom: 50px;
    overflow: hidden;
}
.content_ul li{
    width: 33.3%;
    background-color: #4998e7;
    height: 100px;
    border: 1px solid white;
    float: left;
    text-align: center;
    line-height: 100px;
    color: white;
    font-size: 20px;
}